A start at an adapter for Cassandra via helenus.

Configuration, connection to cassandra nodes, and provisioning
work.  Objects are saved but are not successfully retrieved yet.
The problem is a very naive serialization of sub-objects; I might
switch to just storing json blobs for now.

Dry-coded remove and batch get.
Checkpoint progress on the cassandra adapter layer.

Switched from helenus to scamandrios.
Modified the existing work on the adapter to speak promises.
Improved serialization/deserialization, though I might rip this out
entirely in favor of relying on the marshallers from helenus-thrift.

Document storage & retrieval now works. More or less.
Serialization now mostly uses the helenus-thrift marshallers. We still
resort to JSON.stringify for arrays, hashes, and references.

Column families are now created with column validators appropriate to
the matching model properties.
Fix a race condition in `CassandraAdapter#provision` when creating keyspaces.
Progress on the cassandra adapter: get, update, merge work.
Now on to attachments, which might be annoying.
Batch remove now works. The only remaining errors are attachments, which are unimplemented.
Massive refactor of the Scamandrios adapter.

`CassandraAdapter#provision` may now be called multiple times. The keyspace
and column families will be automatically created if they do not exist.
Attachments (almost) entirely implemented; all tests pass.
This is a lie, because attachments are not deleted when their owner is removed.
YET.
Merging heavily-refactored attachment support.
`CassandraAdapter#link` => `withKeyspace`.
Make `CassandraAdapter#assignKeyspace` fully compatible with pools.
`CassandraAdapter#save`: Automatically create the model and attachments tables.

`createModelTable` and `createAttachmentsTable` will exit early if the tables
already exist.
Implemented removing attachments when documents are removed.
Wrote the unit test for it.
Fixed some bugs as I noticed them.
Travis config tweaks, package.json tweaks.
Merge pull request #11 from ceejbot/cassandra

A working cassandra adapter layer